N-type Indium Gallium Zinc Oxide Research Articles

One-volt oxide based complementary circuit

In low-power electronics, there is a substantial demand for high-performance p-type oxide thin-film transistors (TFTs) that are capable of efficient operation at low voltages. In this study, we employ anodization to form an aluminum oxide gate dielectric layer, enabling the fabrication of p-type tin oxide (SnO) TFTs that effectively operate at a low voltage of 1 V. Under optimal device fabrication conditions, the SnO TFT demonstrates an on/off current ratio exceeding 103 and a saturation mobility of 1.94 cm2 V−1 s−1 at 1 V operation. The optimal SnO TFT fabrication conditions are subsequently used to fabricate a complementary inverter, comprising a SnO TFT and an n-type indium gallium zinc oxide TFT, achieving a gain of up to 38 at a 1 V supply voltage. Notably, the inverter’s switching point voltage is finely tuned to the ideal value, precisely half of the supply voltage. This oxide-based complementary inverter showcases promising potential in low-power electronics.

Ultraflexible Monolithic Three-Dimensional Static Random Access Memory.

Flexible static random access memory (SRAM) plays an important role in flexible electronics and systems. However, achieving SRAM with a small footprint, high flexibility, and high thermal stability has always been a big challenge. In this work, an ultraflexible six-transistor SRAM with high integration density is realized based on a monolithic three-dimensional (M3D) design. In this design, vertical stacked n-type indium gallium zinc oxide thin film transistors and p-type carbon nanotube transistors share common gate and drain electrodes, respectively, saving interlayer vias used in traditional M3D designs. This compact architecture reduces the footprint of the SRAM cell from a six-transistor to a four-transistor area, saving 33% of the area, and significantly enables the SRAM to have the highest flexibility among the reported ones, withstanding a harsh deforming process (6000 cycles of bending at a radius of 500 μm) without performance degradation. Moreover, this design facilitates the thermal stability of the SRAM under high temperature (333 K). It also exhibits great static and dynamic performance, with the highest normalized hold noise margin of 73.6%, a maximum gain of 151.2, and a minimum static power consumption of 3.15 μW in hold operation among the reported flexible SRAMs. This demonstration provides possibilities for SRAMs to be used in advanced wearable system applications.

Oxide Semiconductor Heterojunction Transistor with Negative Differential Transconductance for Multivalued Logic Circuits.

Multivalued logic (MVL) technology is a promising solution for improving data density and reducing power consumption in comparison to complementary metal-oxide-semiconductor (CMOS) technology. Currently, heterojunction transistors (TRs) with negative differential transconductance (NDT) characteristics, which play an important role in the function of MVL circuits, adopt organic or 2D semiconductors as active layers, but it is still difficult to apply conventional CMOS processes. Herein, we demonstrate an oxide semiconductor (OS) heterojunction TR with NDT characteristics composed of p-type copper(I) oxide (Cu2O) and n-type indium gallium zinc oxide (IGZO) using the conventional CMOS manufacturing processes. The electrical characteristics of the fabricated device exhibit a high Ion/Ioff ratio (∼3 × 103), wide NDT ranges (∼29 V), and high peak-to-valley current ratios (PVCR ≈ 25). The electrical properties of 15 devices were measured, confirming uniform performance in the PVCR, NDT range, and Ion/Ioff ratio. We analyze the device operation by varying the source/drain (S/D) position and changing the device geometry and the thickness of the Cu2O layer. Additionally, we demonstrate heterojunction ambipolar TR to elucidate the transport mechanism of NDT devices at a high gate voltage (VGS). To confirm the feasibility of the MVL circuit, we present a ternary inverter with three clearly expressed logic states that have a long intermediate state and greater margin of error induced by wide NDT regions and high PVCR.

Cu2O p-type Thin-Film Transistors with Enhanced Switching Characteristics for CMOS Logic Circuit by Controlling Deposition Condition and Annealing in the N2 Atmosphere

Cuprous oxide (Cu2O) p-type thin-film transistors (TFTs) can be practically applied for complementary metal oxide semiconductor (CMOS) logic circuits, but the electrical performances are still insufficient due to high off-current and low field-effect mobility. Here, we have demonstrated Cu2O TFTs with improved field-effect mobility and low off-current through reduction of cupric oxide (CuO) impurities and dissociative Cu defects with the combination of deposition and annealing conditions. Copper oxide was deposited by radio frequency sputtering in mixed gases of argon and oxygen. After that, the deposited copper oxide was annealed at 800 °C in the tube furnace under a N2 atmosphere instead of a high vacuum condition. The fabricated Cu2O thin film had a high crystalline quality, the ratio of dissociative Cu defects decreased from 11.3 to 3.1%, and the electrical performances of the TFT including the fabricated Cu2O thin film exhibited the field-effect mobility of 1.11 ± 0.05 cm2/V·s, the on/off current ratio of 4.68 ± 0.8 × 104, and the subthreshold swing value of 3.91 ± 0.21 V dec–1. The fabricated Cu2O TFT showed a Vth shift of 3.31 V in the transfer curve under negative bias stress. Nitrogen plays a role in promoting Cu2O phase formation while it prevents CuO phase formation during the annealing process. In addition, oxygen added during sputtering increases the ratio of CuO in the copper oxide thin film and works effectively to reduce dissociative Cu defects in the annealing process. To determine the feasibility of the CMOS logic circuit, we also demonstrated the inverter with n-type indium–gallium–zinc oxide (IGZO) TFT and p-type Cu2O TFT, which showed a voltage gain of 14 at VDD = 20 V.

Imaging Array and Complementary Photosensitive Inverter Based on P-Type SnO Thin-Film Phototransistors

P-type tin monoxide (SnO) thin-film phototransistors were developed with high photoresponsivity of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$2.94\times 10^{{5}}$ </tex-math></inline-formula> A/W and high detectivity of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$1.82\times 10^{{14}}$ </tex-math></inline-formula> Jones, and these values are, to the best of our knowledge, among the highest for the reported oxide-semiconductor-based phototransistors. The excellent performances of these phototransistors were further demonstrated by incorporating the devices into a <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${10}\times {10}$ </tex-math></inline-formula> array to successfully image a letter “A” pattern. Furthermore, by integration of n-type indium gallium zinc oxide and p-type SnO thin-film phototransistors, we realized a complementary photosensitive inverter. The inverter exhibits excellent photoresponse with a high voltage gain rate change of 194%. Our results indicates that the SnO based phototransistors have great potential in thin-film photoelectronic circuits and systems.

Flexible Complementary Oxide Thin-Film Transistor-Based Inverter With High Gain

Wearable bio-sensing devices are considered promising for ubiquitous heath monitoring. To accurately read out small bio-signals, the development of high-performance flexible front-end circuits is crucial. Oxide semiconductors are considered one of the most promising active channel materials for on-polymeric-foil electronics. In this article, a high-gain flexible complementary metal–oxide–semiconductor (CMOS) inverter with a beta ratio of 1, a desirable feature for device miniaturization, was demonstrated by monolithically integrating a top-gated n-type indium gallium zinc oxide (IGZO) thin-film transistor (TFT) and a bottom-gated p-type SnO TFT on a 5.5- $\mu \text{m}$ -thick polyimide substrate. The influence of atomic layer deposited (ALD)-HfO2 capping layer on the properties of oxide active channels has been analyzed. The flexible inverter exhibited a high static voltage gain of 370 V/V and balanced noise margins (noise margin high of 4.8 V, noise margin low of 4.7 V) for a supply voltage of 10 V. In addition, the voltage transfer characteristics remained virtually unchanged when the device was subjected to an outward or an inward bending radius of 2.5 mm, indicating the complementary oxide-TFT-based inverter is practical for flexible electronics applications.

Thin Film Sequential Circuits: Flip-Flops and a Counter Based on p-SnO and n-InGaZnO

Oxide semiconductors have emerged as ideal candidate materials for flexible electronics and circuits. However, complementary flip-flops, which are the essential building blocks in sequential circuits, based on all-oxide thin-film transistors (TFTs) have not yet been demonstrated. Here, we employed n-type indium gallium zinc oxide and p-type tin monoxide to achieve J-K flip-flop (JK-FF) and D-type edge-triggered FF (D-FF). The operation properties of the JK-FF and D-FF were characterised both statically and dynamically. The output signals of the D-FF show great robustness. The D-FF shows very short propagation delay times of 17 and 40 μs from “0” to “1” and from “1” to “0”, respectively. Based on the D-FFs, a two-bit counter with 90 transistors was designed and fabricated successfully, acting as either up-counter or down-counter. To the best of our knowledge, this counter has the highest integration among the reported thin-film complementary sequential circuits based on all-oxide transistors to date.

Micromesh-structured flexible polymer white organic light-emitting diodes using single emissive layer of blended polymer and quantum dots

In this study, poly(N-vinylcarbazole) was blended with CdSe/ZnS core-shell quantum dots of various dimensions to be used as a single emissive layer of flexible polymer white organic light-emitting diodes (WOLEDs). A structure of WOLEDs was deposited on polyethylene terephthalate (PET) substrates. A luminance and maximum luminous efficiency of 4070.2 cd/m 2 and 2.84 cd/A were respectively obtained for the WOLEDs prepared using n-type gallium zinc oxide (GZO) and n-type indium gallium zinc oxide (IGZO) films as the electron transport layer and cathode, respectively. Because the current density can be increased by increasing the carrier transport surface area, the 2-μm-periodic SiO 2 micromesh was fabricated on PET substrates to enhance the surface area of a MoO 3 hole transport layer and a GZO electron transport layer. Furthermore, the GZO electron transport layer could provide a moisture barrier function. Compared with WOLEDs without the SiO 2 micromesh, the prepared WOLEDs had an increased current density of 404.5 (compared with 222.8) mA/cm 2 when operating at 11 V. Moreover, their associated luminance and maximum luminous efficiency increased to 7016.1 cd/m 2 and 3.04 cd/A, respectively. The flexible polymer white organic light-emitting diode (WOLED) with single emissive layer constructed by blending PVK with various dimensional CdSe/ZnS core-shell quantum dots were fabricated and investigated. The 2-μm-periodic SiO 2 micromesh was inserted into the bottom side of the IGZO cathode electrode of the WOLEDs to increase the carrier injection surface area and decrease the carrier propagation length. The luminance and the maximum luminous efficiency of the resulting WOLEDs with SiO 2 micromesh were improved from 4070.2 cd/m 2 and 2.84 cd/A to 7016.1 cd/m 2 and 3.04 cd/A, respectively, in comparison with the WOLEDs without SiO 2 micromesh. • The flexible polymer white organic light-emitting diodes (WOLEDs) was fabricated. • Single emissive layer of blended PVK with quantum dots. • Performance of WOLEDs was improved using 2-μm-periodic SiO 2 micromesh. • Luminance of WOLEDs with SiO 2 micromesh was improved from 4070.2 to 7016.1 cd/m 2 . • Luminous efficiency of WOLEDs with SiO 2 micromesh was improved to 3.04 cd/A.

High-Gain Complementary Inverter Based on Corbino p-Type Tin Monoxide and n-Type Indium-Gallium-Zinc Oxide Thin-Film Transistors

The present work investigated the electrical characteristics of Corbino structure p-type tin monoxide (SnO) thin-film transistors (TFTs) and demonstrated a high-performance complementary logic inverter composed of Corbino p-type SnO and n-type indium-gallium-zinc oxide (IGZO) TFTs. Experimental data showed that the Corbino p-type SnO TFT exhibited an almost infinite output resistance beyond pinch-off in the outer drain condition. The observed phenomenon was mainly attributed to the scaling down of the effective channel width in proportion to the effective channel length. By using the very high output resistance of the Corbino structure TFTs, we fabricated the high-gain complementary logic inverter composed of Corbino p-type SnO and n-type IGZO TFTs. The Corbino TFT-based complementary logic inverter showed a voltage gain of 92.4 at a supplied voltage of 10 V, which was significantly higher than that of 18.7 obtained from the complementary logic inverter composed of the conventional rectangular shaped TFTs.

Oxide-Polymer Heterojunction Diodes with a Nanoscopic Phase-Separated Insulating Layer.

Organic semiconductor-insulator blend films are widely explored for high-performance electronic devices enabled by unique phase-separation and self-assembly phenomena at key device interfaces. Here we report the first demonstration of high-performance hybrid diodes based on p- n junctions formed by a p-type poly(3-hexylthiophene) (P3HT)-poly(methyl methacrylate) (PMMA) blend and n-type indium-gallium-zinc oxide (IGZO). The thin film morphology, microstructure, and vertical phase-separation behavior of the P3HT films with varying contents of PMMA are systematically analyzed. Microstructural and charge transport evaluation indicates that the polymer insulator component positively impacts the morphology, molecular orientation, and effective conjugation length of the P3HT films, thereby enhancing the heterojunction performance. Furthermore, the data suggest that PMMA phase segregation creates a continuous nanoscopic interlayer between the P3HT and IGZO layers, playing an important role in enhancing diode performance. Thus, the diode based on an optimal P3HT-PMMA blend exhibits a remarkable 10-fold increase in forward current versus that of a neat P3HT diode, yielding an ideality factor value as low as 2.5, and a moderate effective barrier height with an excellent rectification ratio. These results offer a new approach to simplified manufacturing of low-cost, large-area hybrid inorganic-organic electronics technologies.

All-Oxide-Semiconductor-Based Thin-Film Complementary Static Random Access Memory

Static random access memory (SRAM) is essential for cache memory. Although oxide semiconductors are ideal candidate materials for next-generation flexible electronics, complementary SRAM based on oxide semiconductors has not yet been demonstrated. Here, we reported an SRAM with a traditional six-transistor structure based on n-type indium gallium zinc oxide and p-type tin monoxide. A cell area of only $\textsf {130} \times \textsf {160}\,\,\mu \text{m}^{\textsf {2}}$ has been achieved and is the smallest among the reported values of SRAMs based on flexible semiconductors. Both traditional static voltage characteristic and N-curve methods are applied to analyze the noise margin level of the cell. The former method demonstrates a high noise margin of 1.43 V in read at ${V} _{\textsf {DD}}$ of 8 V, and the latter demonstrates static current and voltage noise margins of $13~\mu \text{A}$ and 2.05 V, respectively. In addition, the SRAM cell shows rather short writing time of 121 and $82~\mu \text{s}$ for high and low writing states, respectively. This high-performance complementary SRAM based on all-oxide semiconductors indicates its high application potential in large-scale flexible electronics for data storage and processing.

Oxide-Based Complementary Inverters With High Gain and Nanowatt Power Consumption

Oxide semiconductors are ideal candidates for flexible and transparent electronics. Here, we report complementary inverters based on p-type tin monoxide and n-type indium–gallium–zinc-oxide thin-film transistors. The inverters have a gain of 63 at a supply voltage, ${V}_{\text{DD}}$ , of 1.5 V with a maximum static power consumption of 15.6 nW, and a gain of 226 at ${V}_{\text{DD}}$ of 3.0 V with a maximum power consumption of 241.2 nW. A five-stage ring oscillator (RO) based on the complementary inverters is able to operate at 1.04 kHz with full amplitude oscillations at ${V}_{\text{DD}}$ of 1.5 V. All the inverters and RO are fabricated on silicon wafers but at a maximum processing temperature of 225 °C, so that the results are relevant to possible flexible applications. The extremely low power consumption of nanowatt, high gain, kHz operation, and possible flexibility of the fabricated complementary components is well suited to meet the requirements of wearable electronics, Internet of Things technology, and so on.

Room-Temperature Solution-Synthesized p-Type Copper(I) Iodide Semiconductors for Transparent Thin-Film Transistors and Complementary Electronics.

Here, room-temperature solution-processed inorganic p-type copper iodide (CuI) thin-film transistors (TFTs) are reported for the first time. The spin-coated 5 nm thick CuI film has average hole mobility (µFE ) of 0.44 cm2 V-1 s-1 and on/off current ratio of 5 × 102 . Furthermore, µFE increases to 1.93 cm2 V-1 s-1 and operating voltage significantly reduces from 60 to 5 V by using a high permittivity ZrO2 dielectric layer replacing traditional SiO2 . Transparent complementary inverters composed of p-type CuI and n-type indium gallium zinc oxide TFTs are demonstrated with clear inverting characteristics and voltage gain over 4. These outcomes provide effective approaches for solution-processed inorganic p-type semiconductor inks and related electronics.

Hybrid complementary inverter based on carbon nanotube and IGZO thin-film transistors with controlled process conditions

Carbon nanotubes (CNTs) and indium-gallium-zinc oxide (IGZO) have emerged as important materials for p-type and n-type thin-film transistors (TFTs), respectively, due to their high mobility, flexibility, and low fabrication temperature. However, fabricating sophisticated macroelectronic circuits operating in complementary mode is challenging using only a single material, because implementing n-type CNT TFTs and p-type IGZO TFTs is difficult. Therefore, hybrid complementary circuits integrated with p-type CNT TFTs and n-type IGZO TFTs have been demonstrated to combine the strength of each TFT. However, limited efforts have been devoted to optimizing the circuit performance by tuning the process conditions under which the percolated CNT network channel and IGZO channel are formed. In particular, the densities of CNTs in the network channel and the amount of oxygen vacancies in the IGZO channel can be simply adjusted, which are important in determining the electrical properties of each TFT. In this work, we systematically investigated the device and circuit performance by varying such conditions; hence, we confirmed the design features of each TFT that can be optimized to enhance the hybrid complementary circuits.

Highly Optimized Complementary Inverters Based on p-SnO and n-InGaZnO With High Uniformity

Oxide semiconductors are desirable for large-area and/or flexible electronics. Here, we report highly optimized complementary inverters based on n-type indium–gallium–zinc oxide and p-type tin monoxide thin-film transistors. Oxide-based inverters with a record voltage gain of 142 have been achieved. The switching point voltage has also been tuned to reach the ideal value, namely half value of the supply voltage. A narrow transition width of 1.04 V (13% of the supply voltage) is achieved which offers a strong anti-jamming ability to avoid logic errors. Rail-to-rail output voltage swing has been achieved. The inverters still maintain high performance at a low supply voltage of 6 V. A very large number of inverters have been fabricated and showed excellent uniformity in a working area of 1 cm $\times $ 1 cm. The switching point voltage and transition width show very small standard deviations of only 0.55% (0.022 V) and 2.3% (0.024 V), respectively, demonstrating promises for large-scale circuit integration.

Complementary Integrated Circuits Based on p-Type SnO and n-Type IGZO Thin-Film Transistors

Oxide semiconductors are highly attractive for the new-generation transparent/flexible electronics. In this letter, logic gates (inverter, NAND, and transmission gates) and three-stage ring oscillators based on n-type indium-gallium-zinc-oxide (IGZO) thin-film transistors (TFTs) and p-type tin monoxide (SnO) TFTs are presented. The IGZO TFTs show a mobility of 10.05 cm $^{\textsf {2}}$ /( $\textsf {V}\cdot \textsf {s}$ ) and a threshold voltage of 5.00 V. The SnO TFTs exhibit a mobility of 1.19 cm $^{\textsf {2}}$ /( $\textsf {V}\cdot \textsf {s}$ ) and a matched threshold voltage of −5.05 V. At a supply voltage of 10 V, the complementary inverters show an extremely high gain of 112 with a geometric aspect ratio of 5. The dynamic responses of the logic gates based on n-type IGZO and p-type SnO TFTs are also examined. The delay time of the inverter measured from dynamic response is 27.75 $\mu \text{s}$ at a supply voltage of 10 V. The inverter, NAND, and transmission gates all exhibit ideal rail-to-rail output voltage behavior. At a supply voltage of 20 V, the three-stage ring oscillators are able to operate at 32.87 kHz, and the stage delay is $5.07~\mu \text{s}$ .

Enhanced Light Extraction from p-Si Nanowires/n-IGZO Heterojunction LED by Using Oxide–Metal–Oxide Structured Transparent Electrodes

Heterojunction light-emitting diodes (LEDs) comprising p-type Si nanowires (p-Si NWs) and n-type indium gallium zinc oxide (n-IGZO) were fabricated with the different top electrode materials: Al, indium zinc oxide (IZO), and IZO/Ag/IZO oxide–metal–oxide (OMO) multilayer. All the LEDs exhibited typical rectifying behaviors of the p–n junction. Moreover, broad light-emission spectra in the visible range were observed because of the quantum confinement effect (QCE) of the Si NW and Si nanocrystals/nonstoichiometric Si oxide (SiOx) (x < 2) interfaces. In comparison to the LEDs with Al and single IZO electrode, the LED with the OMO multilayer electrode exhibited an enhanced optical performance because the OMO multilayer had an excellent transmittance of 87.7% in the visible range with a low sheet resistance of 5.65 Ω/sq. Furthermore, by investigating the transmittance spectra of the single IZO and OMO multilayer electrodes as a function of the light incidence angle, the OMO multilayer electrode is confirmed to...

Glucose Sensing Using Functionalized Amorphous In-Ga-Zn-O Field-Effect Transistors.

Recent advances in glucose sensing have focused on the integration of sensors into contact lenses to allow noninvasive continuous glucose monitoring. Current technologies focus primarily on enzyme-based electrochemical sensing which requires multiple nontransparent electrodes to be integrated. Herein, we leverage amorphous indium gallium zinc oxide (IGZO) field-effect transistors (FETs), which have found use in a wide range of display applications and can be made fully transparent. Bottom-gated IGZO-FETs can have significant changes in electrical characteristics when the back-channel is exposed to different environments. We have functionalized the back-channel of IGZO-FETs with aminosilane groups that are cross-linked to glucose oxidase and have demonstrated that these devices have high sensitivity to changes in glucose concentrations. Glucose sensing occurs through the decrease in pH during glucose oxidation, which modulates the positive charge of the aminosilane groups attached to the IGZO surface. The change in charge affects the number of acceptor-like surface states which can deplete electron density in the n-type IGZO semiconductor. Increasing glucose concentrations leads to an increase in acceptor states and a decrease in drain-source conductance due to a positive shift in the turn-on voltage. The functionalized IGZO-FET devices are effective in minimizing detection of interfering compounds including acetaminophen and ascorbic acid. These studies suggest that IGZO FETs can be effective for monitoring glucose concentrations in a variety of environments, including those where fully transparent sensing elements may be of interest.

Layer-by-Layer Assembled 2D Montmorillonite Dielectrics for Solution-Processed Electronics.

Layer-by-layer assembled 2D montmorillonite nanosheets are shown to be high-performance, solution-processed dielectrics. These scalable and spatially uniform sub-10 nm thick dielectrics yield high areal capacitances of ≈600 nF cm(-2) and low leakage currents down to 6 × 10(-9) A cm(-2) that enable low voltage operation of p-type semiconducting single-walled carbon nanotube and n-type indium gallium zinc oxide field-effect transistors.

Highly spectrum-selective ultraviolet photodetector based on p-NiO/n-IGZO thin film heterojunction structure.

Ultraviolet photodetector with p-n heterojunction is fabricated by magnetron sputtering deposition of n-type indium gallium zinc oxide (n-IGZO) and p-type nickel oxide (p-NiO) thin films on ITO glass. The performance of the photodetector is largely affected by the conductivity of the p-NiO thin film, which can be controlled by varying the oxygen partial pressure during the deposition of the p-NiO thin film. A highly spectrum-selective ultraviolet photodetector has been achieved with the p-NiO layer with a high conductivity. The results can be explained in terms of the "optically-filtering" function of the NiO layer.